The present invention relates to a retrievable module suitable for a seabed processing system and its use for exploiting oil/gas fields and, more particularly, those underwater.
Conventional oil/gas fields have a plurality of wells linked to a host facility which receives the oil/gas via flow lines. A conventional underwater oil/gas field may include controllable underwater equipment between the wells and the host facility. It would be useful to reconfigure or replace part of the underwater equipment without having to shut down or significantly reduce production from the field.
Such underwater equipment which requires controlling conventionally relies on at least one expensive and complex multiple conduit that provides a hydraulic line to connect each equipment component to a facility on/above the sea surface or onshore.
In the case of wells which are used to extract oil/gas from sub-seabed reservoirs, pressure in the reservoir enables the oil/gas to flow up to the seabed and then on to the host facility. Later in the field life, reservoir pressure can reduce to the point where it is insufficient to allow the oil/gas to flow to the host facility. Current wellhead equipment designed to cope with the initial reservoir pressure cannot be upgraded to suit the subsequent reduction in reservoir pressure. Until now, only individual items of equipment have been identified as having the potential to be removed or replaced and the replacement parts must be designed to fit as before. Underwater processing units cannot be adjusted to suit the changing characteristics of the field.
A further problem is that when well pressure drops below the oil""s so-called bubble point, gas breaks out forming gas slugs, particularly in pipeline undulations. To prevent such slugs forming and subsequently damaging downstream equipment, expensive, high power consumption variable speed motor driven multiphase pumps are required. Such pumps are difficult to control over large xe2x80x9cstep-outxe2x80x9d distances.
A well may be tested by diverting fluid from a well into a dedicated test flow line back to the host facility where it is routed to a test separator and its separated fluids measured. However, it is expensive to provide an additional test flow line.
It is an object of the present invention to provide an improved system which alleviates/solves at least some of the problems mentioned above.
According to the present invention there is provided a retrievable module for a system to which external flow lines are connected, the module including a first portion of a module isolating and connecting means and means for acting on received fluid, comprising at least one inlet flow line for the received fluid and at least one outlet flow line, the at least one inlet flow line and the outlet flow line being connected to the first portion of the module isolating and connecting means for selectively isolating the module from or connecting it to the external flow lines by means of a second complementary portion of the module isolating and connecting means with which the first portion of the module isolating and connecting means is adapted to engage.
There may be provided a plurality of inlet flow lines and one outlet flow line and the means for acting on received fluid interconnects the inlet flow lines and the outlet flow line. The means for acting on the fluid may include a pump.
According to a further aspect of the present invention there is provided a method for acting on fluids in a system to which external flow lines are connected, characterised by the steps of:
providing first and second retrievable modules each module including a first portion of a module isolating and connecting means and first and second means respectively for acting on received fluid in first and second ways respectively, each means for acting on the received fluid comprising at least one inlet flow line for the received fluid and at least one outlet flow line, the at least one inlet flow line and the outlet flow line being connected to the first portion of the module isolating and connecting means for selectively isolating each module from or connecting it to the external flow lines by means of a common second complementary portion of the module isolating and connecting means with which each first portion of the module isolating and connecting means is adapted to selectively engage;
connecting the first module to the processing system;
acting on the fluid received in the first way;
disconnecting the module from the processing system;
replacing the first module with the second module for acting on received fluid in a second way;
connecting the second module to the processing system; and
acting on the received fluid in the second way.
Use of the module isolating and connecting means enables easy diverless module replacement within a short time scale for modification or repair or to change the way a field is exploited to take account of changes in its characteristics such as changes in the mix of fluids it produces and/or a change in the pressure under which the fluids are expelled from the field.
According to a particular aspect of the present invention there is provided a retrievable fluid separation module for a processing system to which external flow lines are connected, the module including a first portion of a module isolating and connecting means and a separator vessel or chamber for separating a plurality of fluids from a received fluid mixture, the separator vessel having at least one inlet flow line for the received fluid mixture and at least one outlet flow line for each separated fluid, the at least one inlet flow line and the outlet flow lines being connected to the first portion of the module isolating and connecting means for selectively isolating the module from or connecting it to the external flow lines by means of a second complementary portion of the module isolating and connecting means with which the first portion of the module isolating and connecting means is adapted to engage.
By having a processing system with a retrievable fluid separation module, the separation of fluids at or near the head of a well on, say, a seabed, avoids multiphase flow problems in flow lines to the host facility, especially where there is a long distance between the well and the host facility. Furthermore, the problem associated with the formation of hydrates in fluid being conveyed to the host facility can be largely avoided, thus largely obviating the requirement for the injection of inhibitors close to the wellhead. Such separation can also lead to an increase of approximately 75% in the total production from a given field.
It may be desirable for the module to include a modulating valve in at least one outlet flow line for controlling flow therethrough and a control actuator for controlling the or each modulating valve. Control means may be provided for controlling operation of the module. The module may have sensing means with an output or outputs connected to the control means. The output from the control means may be connected to at least one of the control actuators for controlling its associated outlet flow line modulating valve. The control means ensures that the level within the separator vessel remain within operating limits by monitoring the level via the sensing means and implementing the operation of the modulating valve accordingly. If abnormal trends or occurrences are detected, then alarm signals are sent to the host facility where manual operation of the processing system can be undertaken.
The control means may be at least substantially an electrical control means or the control means comprises a completely electrical control means. Electrical control means enables the processing system to operate over greater distances/deeper levels, transmit emergency signals instantaneously, such as to shut down a part of the system, and is cheaper to manufacture and maintain.
The sensing means may comprise a fluid interface sensing means for detecting the position of an interface between two of the separated fluids in the separator vessel. Alternatively, the sensing means may comprise means for sensing a plurality of fluid interfaces between three or more separated fluids in the separator vessel.
Conveniently, the module includes pressure measuring means for measuring pressure in the separator.
Chemical injection means may be provided which are connected to the at least one outlet flow line.
The module may have a power connector for connection to a power source remote from the module to provide power for the module. The power connector may have an associated transformer. The power connector may be adapted to carry control signals to or from the module. Alternatively, separate control signal connection means may be connected to the control means, the control signal connection means being adapted to transmit or receive control signals from beyond the module. Use of the power connector and, where necessary, the control signal connection means, enables easy diverless recovery and re-installation of the module within a short time scale for modification or repair.
The retrievable module, by having components for separating fluids, and for control and power all within the module, enables it to be fully pre-tested before being installed in the processing system.
At least one of the separated fluids may be substantially a liquid and the outlet flow line for the liquid includes pumping means. Desirably, the pumping means in the one or more of the outlet flow lines comprises a single speed pump. By having a pump operated by a single speed motor for transport of fluid and using a modulating valve and actuator in conjunction with the sensing means, the need for speed control of large, complex, variable speed multiphase pumps is overcome.
The liquid outlet flow line may have a return branch to the separator downstream of the pumping means. The return branch may have a flow restrictor therein.
The first portion of the module isolating and connecting means may comprise a multiported fluid connector. The multiported fluid connector may have pairs of valves, one valve of each pair being in the opposite portion of the multiported fluid connector to the other valve of the pair.
Conveniently, at least some of the valves are interconnected in a gang so as to be actuatable simultaneously.
A choke valve may be provided in the at least one inlet flow line. The choke valve may have a control actuator. Differential pressure measuring means may be included for measuring differential pressure across the choke valve. The differential pressure measuring means may be connected to the control means which includes means for controlling the choke valve in a manner dependent upon output from the pressure sensing means.
Desirably, the module includes at least one fail-safe valve for controlling flow into the separator vessel. It may be convenient for the fail-safe valve to close in the absence of an electrical signal thereto. At least two such fail-safe valves may be provided in series.
A flowmeter may be provided in the at least one outlet flow line, the flowmeter having an associated flowrate transducer connected to the control means.
At least one separated fluid may be substantially a gas and at least one outlet flow line for the gas may include a gas compressor.
According to another aspect of the present invention there is provided a method for separating fluids in a processing system to which external flow lines are connected, characterised by the steps of:
connecting a retrievable fluid separation module to the processing system;
receiving a fluid mixture in the module from the at least one flow line;
separating in the module a plurality of fluids from the received fluid mixture; and
removing at least some of the separated fluids from the module.
The method may additionally include the step of removing the retrievable fluid separation module from the processing system.
According to a further aspect of the invention there is provided a method for separating fluids in a processing system to which external flow lines are connected, characterised by the steps of:
providing a retrievable fluid separation module including a first portion of a module isolating and connecting means for selectively isolating the module from or connecting it to the external flow lines by means of a second complementary portion of the module isolating and connecting means with which the first portion of the module isolating and connecting means is adapted to engage;
receiving in a separator vessel a received fluid mixture via at least one inlet flow line connected to the first portion of the module isolating and connecting means;
separating in the separator vessel a plurality of fluids from the received fluid mixture; and
removing from the vessel the separated fluids via at least one outlet flow line for each fluid, the outlet flow lines being connected to the first portion of the module isolating and connecting means.
The method may additionally include the step of controlling flow in the at least one outlet flow line by providing a modulating valve therein and a control actuator for controlling the or each modulating valve. Desirably, the method includes the step of detecting the position of a fluid interface between two of the separated fluids in the separator vessel by providing sensing means with an output or outputs connected to control means for controlling operation of the module.
According to yet another aspect of the invention there is provided a modular processing system comprising at least two retrievable at least substantially autonomous modules, and a plurality of module-isolating and connecting means, each retrievable autonomous module being connected to at least one flow line by one module isolating and connecting means, the modules being connected to the at least one flow line and each module is adapted to be isolated from the at least one flow line by its respective module isolating and connecting means without affecting the operation of or the connection of the remaining modules with the at least one flow line. There may be a plurality of flowlines to which the modules are connected in parallel.
There may be a plurality of processing systems connected by the at least one flow line, wherein the isolation of the at least one module by its respective module isolating and connecting means does not affect the operation of or the connection of the remaining modules with the at least one flow line throughout the plural connected processing systems.
According to a further aspect of the invention, there is provided a method for operating a modular processing system, characterised by the steps of:
providing at least two retrievable at least substantially autonomous modules, and a plurality of module isolating and connecting means, each retrievable autonomous module being connected to at least one flow line by one module isolating and connecting means; and
isolating one module from the at least one flow line by its respective module isolating and connecting means without affecting the operation of or the connection of the remaining modules with the at least one flow line.
The system or systems may be substantially on a seabed.